Method for overcoming embrittlement of steel alloys



- States Patent Office Patentedthm 6, 1959 METHOD FOR OVERCOMING EMBRITTLEMEN OF STEEL ALLOYS Application September 23, 1957 Serial No. 685,415

2 Claims. (Cl. 75-1305) No Drawing.

This invention relates to a method for overcoming embrittlemeut of steel alloys, and is particularly useful in combating the embrittlement or cracking tendency known as hot shortness in austenitic stainless cast steels.

This application is a continuation in-part of my copending applications, Serial No. 477,576, filed December 27, 1954, now Patent No. 2,811,438, andSerial No. 485,341, filed January 31, 1955, now abandoned.

In the manufacture of austenitic stainless steels, it is found that the alloys are .difiicult to case, weld, or hot work, without the tendency to be hot short. 'Hot shortness may be defined as a brittleness which occurs in the metal when hot, the metal separating in most cases at the grain boundary. In the casting operation, as the casting cools from the liquid state to the solid state in the mold, the mold sets up a restriction to the contracting metal. Many steels and alloys are strong enough to resist this restriction, but considerable difii culty is found with austenitic stainless steels, and tearing occurs in the casting, which must be welded. Weldingalso becomes a problem, since the metal adjacent the weldis heated, and frequently cracking will occur in this adjoining portion, requiring continual repairs, and eventually the product must be scrapped.

I have discovered that such austenitic stainless steel alloys may be eflectively treated to prevent hot short ness by adding to the alloy while molten a compound of vanadium, titanium and boron. I prefer to add the vanadium and titanium as ferro-compounds, and I find it desirable to employ the vanadium and titanium as a combined ferro-compound. The combination of 'vanadium and titanium in a ferro-compound by molten ag glomeration is well known in the art, and a detailed description herein is believed unnecessary.

The combination of vanadium, titanium and boron may be added to the molten alloy while in the furnace, as, for example, in an arc or induction electric furnace, just before tapping. If desired, it may be added to the ladle during tapping.

, The proportions of the compounds are employed within certain limits which are effective in producing the best results. For example, the vanadium is satisfactorily used in the proportion of 0.02% to 1.07%, the titanium 'in the proportion of 0.01% to 0.6%, while the boron is added in a very small amount, ranging from a trace to 0.002%. I have found that best results are obtained when the vanadium is used in the range of 0.05% to 0.25%, the titanium in the range of 0.01% to 0.15%, and the boron in about 0.002%.

In general, the vanadium employed is about twice that of the titanium, although I find that best results are obtained when the titanium is about three-fifths of the vanadium. I find that all three materials, namely, the vanadium, titanium and boron, cooperate in eliminating the hot shortness, and when used in the percentages shown, the finished tested product shows practically no cracks 3 even after the flame test and Zyglo inspection.

In the test generally referred to as the flame test, one end of the specimen is subjected to a torch for one minute, and thereafter a green fluorescentpenetrant dye is applied anddeveloped so as to disclose the presence of minute cracks, etc. Since such tests are well known, a detailed description herein is believed unnecessary and it is suflicient to say that under such rigorous tests the products treated in accordance with the present invention disclose very few, if any, perceptible cracks.

In the operation of the process, the austenitic stainless steel alloy is brought to a'molten condition within the furnace and the ferro-compound of vanadium and titanium and the boron are added to the metal in the furnace or, if desired, to the ladle during tapping. Aluminum may be added in the deoxidizing procedure, in accordance with general furnace practice, and silicon may also be added for the maintenance of the physical properties and to promote fluidity. If desired, the alu minum and silicon may be added simultaneously with the titanium, vanadium and boron, and the proportions of these will be the proportions usually added according to general furnace practice.

Specific examples of the process may be set out as follows:

Example I A stainless steel alloy having the following analysis:

, I Percent Carbon max 0.07 Manganese 2.00

' Silicon i max 1.5 Chromium 20.5 Nickel 29.3 Molybdenum 2.4 Copper "L 3.3

The operation was carried on as described in Example I, except'that thevanadium was in the proportion of 0.25%, the titanium in the proportion of 0.15%, the boron remaining at about 0.002%. The results obtained were comparable to those described in Example I. Example III The process was carried out as described in Example I except that the austenitic stainless steel had a different composition, containing 24% chromium, 20.5% nickel, 0.08% carbon, about 1.5% manganese, and 1.0% silicon. The procedure as described in Example I was found to eliminate hot shortness in the above-described alloy.

Example IV The process was carried out as described in Example I, except that the stainless steel alloy treated had about 17.65% chromium content, 13.65% nickel, 2.65% molybdenum, 0.08% carbon maximum, about 1.25% manganese, and about 1.0% silicon. Hot shortness was eliminted by the adding of the materials described in Example I.

Example V The process was carried out as described in Example IV, except that the stainless steel alloy treated had about 1 8.7% chromium and 10.5% nickel, the carbon, man'- ganese, and silicon contents being the same as shown in Example IV. Comparable results were obtained.

Example VI boron, appear to produce together, as a total eflect, the

elimination of the hot shortness, and while the proportions of these may be varied wtihin a substantially wide range depending upon the analysis of the-particular austenitic cast stainless steelmaterial being treated, the important new, result of eliminating hot shortness is achieved by the use of all three'ma-ter-ial's.

Both corrosion-resistant and heat-resistant cast stainless steels are materially improved through the procedure of this invention. A distinction between the two steels is that the corrosion-resistant steels are generally used to resist attack at temperatures less than 1200 F., while heat-resistant alloys are generally used under-conditions where the metal temperature is in excess of 1200 F. I have found that in the instance of both corrosionresistant and heat-resistant stainless steel castings, a favorable cooperation between vanadium, and titanium occurs to substantially eliminate hot shortness.

Exemplary of the practice of the invention in this connectionarethe-following-examplesr Example VII V p i A stainless steel alloy having the following analysis:

was heated in an electric furnace to molten condition,

' and to the molten metal just before tapping was added ferro-vanadium and titanium in the proportions of 0.05% vanadium and 0.01% titanium. The casting test bars made from the alloy were subjected to the flame test and to the fluorescent dye penetrant (Zyglo), and it was found that there were practically no perceptible cracks, thus showing the elimination of hot shortness.

Example VIII The operation was carried on as described in Example VII, except that the vanadium was in the proportion of 0.25%, and the titanium in the proportion of' 015%. The results obtained were comparable to. those described in Example V11".

Example IX The process was carried out as described in Example VII, except that the austenitic stainless steel had a slightly different composition, containing 21% chromium and 12% nickel instead of the percentages set forth for these elements in Example VII. The procedure as described in Example VII was found to eliminate hot shortness in the above-described alloy.

Example X The process was carried out as described in Example I, but with a stainless steel alloy having the following composition:

Percent Carbon 0.20 Manganese 2.0

, Silicon 2.0 Phosphorus 0.04 Sulphur 0204 Chromium 24.0

Nickel 18.0 Molybdenum max 0.5

Hot shortness was eliminated by the adding of, the. material described in, Example VII.

Example XI The process was carried out as described in Example X except that the stainless steel alloy treated had; 28% chromium and 22% nickel instead of the amounts of these elements. specified in- Example Comparable results wereobtained'.

While in the foregoing description, I, have set forth in detail specificsteps and proportions for the purpose of illustrating preferred embodiments of the invention, it will be understood. that such details of procedure, prQ- portions, etc., may be varied widely by those skilled. in the art Without departing from the spirit of my invention.

I claim: v

1. In a process for preventing hot shortness in an austenitic cast stainless steel alloy, thesteps of heating the alloy to bring it to a molten state and then adding vanadium and titanium combined in: a-,ferro-compound, the proportions of the vanadium being .05 to .25%, and of the titanium .01 to .15%.

2. In a process for preventing hot shortness in an austenitic cast stainless steel alloy, the steps of heating the alloy to bring ity to a molten state and then. adding to the molten alloy vanadium and titanium. simultaneously, the proportion of the vanadium being; .05 to 25%, and of the titanium .01 to .15%

References Cited in the file of this patent UNITED STATES PATENTS 1,542,232 Girin June 16, 1925 2,432,617 Franks et a1 .4..... Dec. 16, 1947 2,602,028 Urban et al'. July 1, 1952 2,750,283 Loveless June 12, 19.56 2,811,438 Fink Oct. 29, 1957 

2. IN A PROCESS FOR PREVENTING "HOT SHORTNESS" IN AN AUSTENITIC CAST STAINLESS STEEL ALLOY, THE STEPS OF HEATING THE ALLOY TO BRING IT TO A MOLTEN STATE AND THEN ADDING TO THE MOLTEN ALLOY VANADIUM AND TITANIUM SIMULTANEOUSLY, THE PROPORTION OF THE VANADIUM BEING .05 TO .25%, AND OF THE TITANIUM .01 TO .15%. 